1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and an image processing program.
2. Description of the Related Art
Drawing data written in a Page Description Language (PDL) such as PostScript (registered trademark) or PDF (Portable Document Format) is input into an image forming section of an image forming apparatus or an apparatus solely used for image formation (hereinafter collectively referred to as the image forming apparatus). The input drawing data consists of a set of objects of different types (drawing objects to be drawn), including graphics, text, and other types of images. The drawing data is interpreted in the image forming apparatus and image data is generated for each page. Interpretation of drawing data in the image forming apparatus typically involves a large number of computations depending on the complexity of the data. In the image forming apparatus, image data for each page such as a raster image page or a compressed image is generated based on the drawing data. The image data generated on the image forming apparatus (e.g., the image forming section of the image forming apparatus) undergoes image processing such as page merging or rotation as required, which is performed by an image processing section of the image forming apparatus or an apparatus solely used for image processing, and is then sent to a printer engine and printed.
To increase the rate of printing, the time required for image formation and the time required for image processing must be minimized as much as possible.
Parallel processing in which image processing processes are performed in parallel and concurrently is effective for minimizing the time required for image processing. Examples of parallel processing include a method in which image data of multiple pages is processed in parallel on a page basis and a method in which a raster image output from the image forming apparatus is split into tiles, which are then processed in parallel.
Splitting a page image into tiles for parallel image processing is also known but has a problem that, when a horizontally oriented image is to be split, the image can be split only after all scan lines are provided.
The just-mentioned methods solely intended for high-speed processing of image data cannot increase the speed of image formation processing to form image data from drawing data, which is load-intensive processing.
Therefore, an approach has been devised in which the processes of image formation processing are parallelized to speed up image formation processing. For example, an apparatus has been disclosed which splits a drawing object into lines or strips in the horizontal direction and performs parallel processing on the horizontally split object to be drawn (see for example European Patent No. EP0860768). Another image processing apparatus has been disclosed which splits a two-dimensional region to be drawn into blocks (see for example Japanese Laid-Open Patent Publication (Kokai) No. H04-170686).
Yet another approach is to pipeline the processes of image formation processing (see U.S. Pat. No. 6,483,519).
However, the conventional image forming apparatuses that split an object to be drawn into horizontal lines or strips has a problem that processing for printing an image, in particular a horizontally long image, takes much time.
An alternate approach that is suitable for tile-based parallel processing to speed up image formation processing may be to segment drawing data into blocks. In such a case however, intersections of all the drawing objects to be drawn contained in a page and the boundary of each block must be precisely calculated in order to identify drawing objects contained in PDL data for each block. The calculation of intersections is sequential processing because the order in which the objects are drawn must be stored, resulting in a problem that the block segmentation involves much computations and requires much time.